496 Pirsson and Washington — Geology of New Hampshire. 



has already shown the close relationship between the rocks 

 classed as camptonites and essexites, showing that the former 

 could be derived from the latter by differentiation, and that 

 since the volume of the complementary bostonite is relatively 

 small, that of the essexite and camptonite are practically alike. 

 If indeed in Gran the essexite magmas had been subjected to 

 the same processes of cooling and crystallization, in undiffer- 

 entiated condition, as those which produced the camptonites, it 

 can scarcely be doubted that they would have produced essen- 

 tially similar rocks which would also be termed camptonites. 



Mode. — The mode or actual mineral combination was 

 determined by Rosiwal's method. For the coarse-grained type 

 of the main mass a large section measuring 30x40 mm of rock 

 surface was used and a distance of 200 times the average grain 

 was traversed. The border facies was also measured and the 

 results obtained are given in the table. 



Vol. per cents. Weight per cents. 



Border. Main. Border. Main. 



Apatite 1*9 0'6 1-9 0*6 



Titanite _.. 0'3 2-2 0*3 2-2 



Iron ore __ 4 5 7.7 7-6 12*5 



Pyroxene.. 4-3 15-8 4*6 16'1 



Biotite 10-7 3-3 10-4 3*1 



Hornblende 27-6 26*3 30'6 27*9 



Plagioclase . . _ 47*1 43*5 41*6 36*6 



Scapolite 2-9 2*4 



Epidote 0-6 0*6 



Chlorite _ 0*6 0*6 



Total 99-9 100-0 100*0 99'6 



Classification in the Quantitative System. — The calculation 

 of the norm of this rock from the analysis and the determina- 

 tion of its systematic position are given in the subjoined table. 



Norm. 



., "" no . n1 == =— — = 1-5 = Class 3, Salfemane 



Ab .. 22-01 Fern 39-2 ' 



An .. 26-69 L 1-4 



Ne . . . 1-42 fr = 5T6 = °'° 2 = ° rder 5 ' Gallare 



Di... 13-38 K a O' + Na a O' 63 



Ol 10 47 CaO' = 96 = ' = g ' Cam P tonase 



Mt _.. 5-80 K 2 0' 16 ao . _ , A n 



II ... 7-90 Na( y = 4 ? = °' 34 > = Subrang 4, Camptonose 



Ap ._ 1-68 

 Rest _ 1-64 



Total.. 99-89 



